1. Field of the Invention
The present invention relates to a rain cover attached to an ignition plug attaching hole formed in an engine head of an automobile engine for the purpose of preventing drops of water from entering the ignition plug attaching hole. More particularly, the present invention relates to an improved rain cover of an ignition plug attaching hole by which drops of water do not enter the ignition plug attaching hole through a vent hole formed through the rain cover and communicating a space inside the ignition plug attaching hole with the atmosphere.
2. Description of the Related Art
Conventionally, a plug cap is used for connecting a high tension cable for supplying a high voltage current to an ignition plug of an automobile. In this connection, in the case of a Dual Over-Head Cam (DOHC) engine having two cam shafts for opening and closing the valves on the engine head, the ignition plug is attached at a bottom portion of the ignition plug attaching hole provided on the engine head.
Accordingly, a plug cap used for the DOHC engine is formed long and slender, so that the high tension cable can be connected with the ignition plug attached at the bottom of the ignition plug attaching hole. A rain cover, liquid-tightly engaged in the ignition plug attaching hole, is provided so that drops of rain water do not enter the ignition plug attaching hole.
FIG. 3 is a view showing an example of the plug cap for use in the DOHC engine described above. This plug cap 5 includes: a high tension cable 21; a long and slender cylindrical insulator 20 accommodating a connection terminal 22 for connecting the high tension cable with an ignition plug 3; and a rain cover 10 attached at an end of this insulator 20 for liquid-tightly sealing the ignition plug attaching hole 2. This plug cap 5 is attached to an engine head 1.
As shown in FIG. 4, the rain cover 10 is externally engaged with the insulator 20. The rain cover 10 includes: a cylindrical portion 11, the lower end of which is engaged with an inner circumferential surface of the ignition plug attaching hole 2; a disk-shaped flange portion 13 having a contact portion 14 concentrically provided on an outer circumferential surface of the cylindrical portion 11 so that the contact portion 14 comes into contact with an outer surface of the engine head 1; and a protrusion 12 protruding outward from a head of the cylindrical portion 11 in a radial direction with respect to an axis of the ignition plug attaching hole 2.
A cutout portion 15 is formed on a surface of the cylindrical portion 11 at a base end of this protrusion 12. An opening of the vent hole 16 on the atmosphere side faces this cutout portion 15 so that an inner space of the ignition plug attaching hole can be communicated with the atmosphere. Because of the above construction, even when air in the ignition plug attaching hole 2 is expanded by the heat of an engine, the plug cap 5 is not disengaged from the ignition plug attaching hole 2 by the pressure of expanded air, so that the plug cap 5 is not disconnected.
Although the conventional rain cover 10 possesses a profile having an excellent appearance and a high workability of attaching the plug cap 5 to the engine, the following problems may be encountered.
As shown in FIG. 4, an amount of protrusion of the protruding portion 12 covering the cutout portion 15 facing the opening of the vent hole 16 on the atmosphere side is small, and an outer end portion of this protruding portion 12 is connected with the cutout portion 15 by a gently curved surface. Therefore, drops of water adhering to the protruding portion 12 easily flow into the cutout portion 15 as illustrated by an arrow in the drawings.
Further, since an interval between the cutout portion 15 and the flange portion 13 is small, a drop of water W adhering to the base end of the flange portion 13 tends to enter the cutout portion 15. Furthermore, since the flange portion 13 is formed flat, it is difficult for the drop of water W adhering to this flange portion 13 to flow down onto the outer circumferential side of the flange portion 13.
Because of the above construction, when the rain cover 10 gets wet on a rainy day or when the car is washed, drops of water enter the ignition plug attaching hole 2 through the vent hole 16. Therefore, a high voltage current to be supplied to the ignition plug 3 leaks, so that the ignition plug can not be ignited.